This invention relates to a parallel-bivalent apparatus which operates as an absorber-heat pump and as a boiler for heating a heat carrying medium. The apparatus includes an expeller which is also part of the boiler, a condenser, an evaporator and an absorber. The absorber through which the heat carrying medium passes, is supplied with a poor solution by the expeller, with the intermediary of a heat exchanger for poor and rich solution and an expansion value.
As opposed to known apparatus operating in the alternative-bivalent mode wherein at higher external temperatures (temperatures of the intake air) only the heat pump works and in case of lower temperatures below 0.degree. C. only a conventional heater (containing the boiler) operates, an apparatus operating in the parallel-bivalent mode has the advantage that even at relatively low intake air temperatures the absorption heat pump is operative and the additional heat supplied by fuel has to be designed only to cover the output difference between the required heat output and the output delivered by the heat pump.
An apparatus operating in the parallel-bivalent mode of the above-outlined type is, in principle, disclosed in German Laid-Open Application (Offenlegungsschrift) No. 2,647,216 which, however, describes in detail only an apparatus equipped with a compression heat pump.
If the heat pump of the apparatus is to operate economically even at relatively low intake air temperatures, for example, at -15.degree. C., the output of the heat pump has to be increased as compared to known arrangements.